1. Field of the Invention
The present invention relates to a refrigerant compressor with cooling means for use, for example, in an automotive air conditioning system.
2. Description of the Related Art
FIG. 8 illustrates a part, i.e., a drive power transmission unit, of a typical refrigerant compressor according to the prior art. The compressor has a housing 101 accommodating a compression mechanism not shown, therein. A drive shaft 102 is operatively connected to a compression mechanism, and has a part projecting outside from the housing 101 to receive a drive power from an external drive power source. A shaft seal member 103 is mounted in the housing 101 for making a sealing contact with the outer circumference of the drive shaft 102. The drive shaft 102 is connected to a vehicle engine 104, via a solenoid clutch 105 and a pulley belt 106 which form the drive power transmission unit. When the solenoid clutch 105 is energized to provide a mechanical connection between the vehicle engine 104 and the drive shaft 102 during the operation of the vehicle engine 104, the drive shaft 102 is driven for rotation, so that the compression mechanism compresses a refrigerant gas.
The solenoid clutch 105 has a rotating hub-like plate 107 fixedly mounted on the part extending outside the housing 101 of the drive shaft 102, a pulley-like rotor element 108 supported for rotation on an outer wall surface of the housing 101, a core 109 disposed inside the rotor element 108, and an armature 111 supported on the rotating plate 107 by a flat spring 110. The armature 111 is pressed on the rotor 108, against the resilience of the flat spring 110, by a magnetic attraction generated by electro-magnetically energizing the core 109 to transmit a drive power from the rotor 108 to the rotating plate 107 fixed to the drive shaft 102.
FIG. 7 shows a part of a clutchless-type compressor different from the afore-mentioned clutch-accommodating type compressor and provided with a drive power transmission unit having no clutch mechanism between a vehicle engine 104 and a drive shaft 102. The drive power transmission unit of the clutchless type compressor has a pulley element 112 instead of a solenoid clutch 105. The pulley element 112 is combined with a bushing 113 fixed to a front end part of the drive shaft 102 projecting outside a housing 101, and a rotor member 114 around which a belt 106 driven by the vehicle engine 104.
The drive shaft 102 is in sliding contact with a shaft seal 103 similar to the shaft seal 103 of the compressor of FIG. 8. The shaft seal 103 is heated up to a high temperature by friction between the rotating drive shaft 102 and the shaft seal 103 and therefore, a part of the heat generated in the shaft seal 103 is dissipated through the drive shaft 102 at a portion thereof extending outside from the housing 101. In the clutchless type compressor of FIG. 7, the bushing 113 and the rotor 114 combined together, and hence heat is transferred at high heat transfer efficiency from the bushing 113 to the rotor 114. Accordingly, it can be expected that heat transmitted by the drive shaft 102 outside the housing 101 is radiated from the bushing 113 and the rotor 114 at a high efficiency, i.e., the entire pulley 112 exhibits a high heat-radiation effect. Consequently, the lifetime of the shaft seal 103 is extended and the shaft seal 103 can maintain its satisfactory function to seal the clearance around the drive shaft 102 for an extended period of use.
Nevertheless, in the clutch-accommodated type compressor of FIG. 8, the rotating plate 107 and the rotor 108 of the drive power transmission unit are separate members, and the rotating plate 107 and the rotor element 108 are connected by the flat spring 110 and the armature 111. The flat spring 110 consists of a thin plate so that it is elastically deformable and accordingly, forms a passage of a only small sectional area to transmit heat from the rotating plate 107 to the rotor 108. Thus, it is understood that the flat spring 110 is an impediment to heat transmission which reduces the efficiency of heat transmission from the rotating plate 107 to the rotor 108. Consequently, the heat dissipating effect of the rotor 108 having a large surface area is not as much as expected, and the heat radiating effect of the solenoid clutch 105 is rather small.
Further, in some recent clutchless type compressors, not shown, a pulley similar to the pulley element 112 of FIG. 7 is constructed by a combination of a bushing and a rotor which are similar to the elements 113, 114 of FIG. 7. However, the bushing and the rotor element are elastically connected by a damping member or members made of a synthetic rubber. The damping member elastically deforms so as absorb a variation in the load torque which is generated in the compression mechanism of the compressor.
In such a clutchless type compressor, the damping member of the drive power transmission unit is impediment to heat transmission and reduces the efficiency of transmission of heat from the bushing to the rotor element because the thermal resistance of the synthetic rubber is greater than those of metals. Consequently, the heat radiating effect by the rotor element of the drive power transmission cannot be very large, and the heat radiation effect exhibited by the pulley 112 is small, and accordingly, cooling of the compressor is insufficient.